The Base libraries provides us the fundamental features and functionality of the Java platform.
Lang and Util package provides the fundamental classes and Object of primitive type, a basic math class etc. It also provide wrapper class.
Math functionality includes floating point libraries and arbitrary-precision math.
Monitoring and Management
Monitoring and Management API provide support to JVM, for the Logging Facility, jconsole and Java Management Extensions (JMX), and Sun's Platform Extension etc.
Package Version Identification
Using this feature , the applets and application can identify the version of JRE, JVM and class package or in other words we can say that this feature provides us the package-level version control.
A reference object provide us reference to some other object. Later, the referenced object can also be incorporated by collector. It also provide a bounded interaction with the garbage collector.
Reflection enables Java code to discover information about the fields, methods and constructors of loaded classes, and to use reflected fields, methods, and constructors to operate on their underlying counterparts on objects, within security restrictions.
This framework provide support for representation of the collections including their manipulation. This framework cut down effort by enhancing performance.
Concurrency Utilities package giving us a efficient framework of high-performance threading utilities. Some example are blocking queues and thread pools.
Java Archive (JAR) Files
The jar file provide us file contraction which reduces download time. The most important feature is that it is platform independent.
Using this API you can create log reports which can help in analysis , servicing and maintainance.
Using This API , you can save and fetch/ retrieve preferences of system and user and also data of configuration.